Wet spun cellulose triacetate



3,057,039 WET SPUN CELLULOSE TRIACETATE Jesse L. Riley, New Providence, N.J., assignor to Celanese Corporation of America, New York, N.Y., a corporation of Delaware Filed Apr. 21, 1958. Ser. No. 730,021 Claims. (Cl. 28-82) This application is a continuation-in-part of my earlier copending application Serial No. 638,414 filed February 5, 1957.

This invention relates to the spinning of cellulose triacetate to form filamentary materials.

Textile materials of cellulose triacetate have recently attained considerable commercial importance. On suitable treatment, these textile materials have superior heat resistance, high safe-ironing temperatures, excellent wash fastness even when dyed in heavy shades, crease-resistance and resistance to glazing and to shrinkage on pressing with moist steam. However, the strength of the cellulose triacetate filaments used in such textile materials has not been as high as desired. Typical cellulose triacetate filaments, whether produced by dry spinning a solution of the cellulose triacetate into an evaporative atmosphere or by wet spinning this solution into a liquid coagulant, have had tenacities of the order of 1.3 grams per denier, with elongations at break in the vicinity of 25-30%. Materials having these properties are satisfactory for use in continuous filament form, but they are not so suitable for use as staple fibers where higher strengths are desirable.

It is therefore an objective of this invention to provide novel, much stronger cellulose triacetate filamentary material and a new process for making such materials.

Another object of this invention is the provision of a new method for the wet spinning of cellulose triacetate.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims, all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention, a solution of cellulose triacetate in a solvent comprising methylene chloride is extruded through a spinning orifice into a non-solvent bath, hereinafter termed a spin bat containing methylene chloride and a lower aliphatic alcohol, preferably methanol, and the resulting swollen filamentary material is stretched in the spin bath. I have found that, for any given set of spinning conditions, there is a certain ratio of methylene chloride to the alcohol in the spin bath at which the tensile strength and elongation at break of the resulting filamentary material are both at their optimum values. That is, when curves are drawn relating tenacity and elongation, respectively to the concentration of methylene chloride in the spin bath, all other factors being the same, both curves reach their maximum values at about the same concentration of the methylene chloride, generally when the bath contains about /2 methylene chloride, or otherwise stated, when the ratio of methylene chloride to methanol is in the neighborhood of 1:1.

The mechanical properties of the filamentary material obtained according to the process of this invention are superior to anything heretofore attained by the wet-, dry-, or melt spinning of cellulose triacetate. Thus, the products of this invention have tenacities of over 1.8, 2 or higher, grams per denier accompanied by elongations of over 18%, e.g. 20% or higher, even for filaments whose denier is in the range of 1.5 to 4. The energy of rupture, i.e. the area under the stress-strain curve from zero stretch to break, is high, above 16,500 dyne cm. for 1 cm. of a 3 denier filament. These filamentary materials are characterized by radical uniformity. This can be determined by treating the fila-mentary materials with a saponifying agent which deesterifies the surface portions of the tates atent I" filamentary material, forming a cellulose skin which is then removed with a solvent for cellulose. When subjected to this treatment a filamentary material which is non-uniform exhibits different properties as compared with the original material, while a radially uniform material has the same properties as before.

In testing for radial uniformity the surface removal can be eifected, for example, by wetting the filaments to be tested in cold water containing 0.1 gram per liter of Triton X-lOO (iso-octyl phenyl ether of polyethylene glycol), then immersing them in 1000 times their weight of a 50 grams per liter solution of sodium hydroxide at C. for from 30 seconds to 3 minutes, and quickly transferring them to cold running water for 5 minutes. The filaments are then soured in acetic acid for 15 minutes and again rinsed in running Water for 15 minutes. After drying in air, the filaments are immersed at room temperature for 3 minutes in a solution made up of equal weights of cupriethylene diamine and water to dissolve the cellulose skin formed by the saponification. The filaments are then rinsed, soured, rinsed and dried as before.

The foregoing treatments of course reduce the filament denier but the tenacity in grams per denier is not changed.

The percent elongation also remains unchanged. X-ray diffraction patterns, microscopic observations and other properties are also the same for the starting material and for specimens from which surface layers of different thickness are removed. The safe-ironing temperature following heat treatment is also the same whether or not the filament is de-surfaced,

Whereas surface removal of dry spun cellulose triacetate effects a marked increase in the rate of dyeing, surface removal of cellulose triacetate filamentary material wet spun in accordance with the present invention does not similarly aifect the dyeing rate. This is demonstrated as follows: Dry spun cellulose triacetate filaments of 3.75

denier when immersed in a dyebath took up 0.18% of their weight ofdyestuff after being immersed in the dyebath for 5 minutes and 0.22% of their weight after 15 minutes immersion. If these filaments are first treated as described to remove a surface layer 44 10- cm. thick, the filaments under identical dyeing conditions will pick up 0.22% by weight of dyestulf in 5 minutes and 0.30% in 15 minutes. This appreciable increase in pick up evidences radial heterogeneity in the filaments.

By way of comparison, 2.5 denier filaments produced in accordance with the invention pick up 0.24% by weight of dyestulf after being immersed 5 minutes in the dyebath previously set forth and 0.34% after 15 minutes. Removal of a surface layer 47 10 cm. thick does not increase the dyeing rate. Actually there is a slight decrease to 0.23% and 0.31% in 5 and 15 minutes, respectively, i.e. approximately the same rate as de-surfaced dry spun cellulose triacetate filaments. This slight decrease in the dyestutf pick up rate of de-surfaced wet spun filaments produced in accordance with the present invention as opposed to wet spun filaments which have not been de-surfaced is due to the fact that the wet spun filaments initially have a slightly pebbled surface which is smoothed out upon tie-surfacing thereby reducing slightly the surthe range of about 0.034 to 0.037. This overall hire-- fringence is the sum of the birefringences through the fiber and is measured, in conventional manner, by a transmission technique. In the complete saponification method employed for this purpose, the filamentary material is saponified completely by immersion for at least 30 minutes in times its weight of a solution containing, by weight, parts of sodium hydroxide, 12 parts of sodium acetate, parts of dimethylsulfoxide and 73 parts of water, at 80 C. Completion of saponification can be checked by Wetting the filamentary material with 1-N cupriethylene diamine solution; if, as viewed under a microscope, the filamentary material dissolves completely in 30 seconds, saponification is complete; if not complete, the time of immersion in the saponifying liquor can be increased. When it has been determined that saponification is complete, the filamentary material is rinsed with distilled water until the rinse water is neutral. The saponified material is air dried; the treatment does not cause shrinkage or loss of strength. The overall birefringence, as opposed to merely surface birefringence, is determined in customary manner, as with a Berek compensator using polarized light.

Cellulose triacetate filamentary materials produced in accordance with this invention exhibit definite rubbery properties at elevated temperatures. This is demonstrated in the following manner: A 125 denier 40 filament yarn is held at constant length (e.g. 10 inches) and heated to a temperature of 220 C. at a just perceptible initial tension (about 0.039). The temperature is then cycled between 217 C. and 223 C. It will be found that the tension on the filament increases as the temperature increases and decreases very perceptibly as the temperature decreases, typical of a rubber. By way of comparison, if the temperature of the filament is cycled between 162 C. and 168 C., the tension will be found to decrease as the temperature increases, typical of a glass.

Like other cellulose triacetate filamentary material, the cellulose triacetate filamentary material obtained in accordance with this invention may be heat treated to raise the safe ironing temperature of fabrics produced therefrom and to improve the dimensional stability, resistance to creasing, permanence of pleating, and the like. However, the filamentary material of this invention shows substantially n0 shrinkage or decrease of tenacity on such heat treatment. In fact, the tenacity may even increase. For example, a filament produced in accordance with ths invention and having an original tenacity of 2.15 grams per denier, when heat treated in air at 210 C. for 5 minutes shrinks less than 1% and has a final tenacity of 2.37 g./den.

Cellulose triacetate filamentary material produced in accordance with the invention is also characterized by resistance to creep at elevated temperature. This is demonstrated as follows: 0ne end of a filament is anchored within a horizontal heating tube. 10 inches from the anchored end, the filament is knotted to a glass filament which extends outside the tube and runs over a pulley. A weight is suspended from the protruding end of the glass filament. With various size weights suspended from the glass filament the tube is heated and the displacement of the weight with change in temperature is noted. Cellulose triacetate filaments produced by dry spinning the initial solutions begins to creep at about 168 C. The instant filamentary materials do not creep comparably below about 178-183 C. The rate and amount of creep for dry-spun filaments under a load of 0.033 gram per denier are only reached for the instant filamentary materials at a load equal to or in excess of 0.067 gram per denier.

The products are highly suitable for the manufacture of textile materials of staple fibers, as well as textile materials made of continuous filaments. The spinning procedure of this invention has given excellent results not only for the spinning of one filament from one spini nerette, but also for the spinning of thousands of parallel filaments from a single multi-apertured spinnerette.

The cellulose triacetate employed in accordance with this invention has an acetyl value of at least 60%, preferably above 61%, calculated as acetic acid. It is preferred that the intrinsic viscosity of the cellulose triacetate be in the range of about 1.5 to 3, best results being obtained when the intrinsic viscosity is at least about 2. The intrinsic viscosity referred to above is the intrinsic viscosity of the regenerated cellulose obtained by completely saponifying, without degradation, the cellulose triacetate. The intrinsic viscosity of the regenerated cellulose is determined according to well-known accepted procedures, using a solution of the regenerated cellulose in cupriethylenediamine.

The cellulose triacetate is dissolved in methylene chloride either alone or, for best results, in admixture with a small amount of a lower aliphatic alcohol, preferably methanol. The proportion of methanol in the solvent mixture may be varied, up to about 15% of the solvent mixture. As for the concentration of cellulose triacetate in the spinning solution, excellent results have been ob tained within the range of 18 to 26%, about 20-23% being preferred. The concentration of cellulose triacetate is desirably such that the viscosity of the solution is about 500 to 6,000 poises at the spinning temperature, i.e. the temperature at which the solution is extruded into the spin bath of methylene chloride and lower aliphatic alcohol. The spinning temperature is desirably in the range of about 15 to 45 (3., though when operating at atmospheric pressure it is preferable to use a temperature below 40 C. to avoid formation of bubbles of solvent.

The optimum proportions of methylene chloride and the methanol or other lower aliphatic alcohol in the spin bath will vary depending on the temperature of spinning, other conditions of spinning being kept constant, the methylene chloride concentration being reduced as the temperature is raised and increased when the temperature is lowered. By these changes in proportions with changes in temperature the power of the bath to swell the cellulose triacetate is maintained substantially constant. In place of the methanol other alcohols, such as ethanol, n-propanel or isopropanol, may be employed, but the results are not as good as when methanol is used.

It is found that, other conditions being the same, there is a substantially linear relationship between the temperature of spinning and the optimum concentration of methylene chloride in the spin bath. Thus, in one series of experiments, spinning 40 filaments simultaneously through orifices 0.1 mm. in diameter in a single spinnerette, the optimum spin bath at 25 C. contained 50% methylene chloride and the balance methanol; at 29 C. it contained 46% methylene chloride; and at 35 C. it contained 41% methylene chloride. Under the same conditions, but spinning 1440 filaments simultaneously from one spinnerette, at 26 C. and 32 C. the optimum spin baths contained 49.5% and 42.5% methylene chloride respectively. Plotting these data on a graph shows all these points to be substantially on one straight line. The above series of experiments was carried out using a 21.5% solution of cellulose triacetate of acetyl value 61.5%, calculated as acetic acid, and intrinsic viscosity 2.0, dissolved in a mixture of 90 parts of methylene chloride and 10 parts of methanol, the filaments being taken up at the rate of meters per minute, at draw-down ratios of 10:1 to 5:1, and the denier of the resulting filaments being in the range of 2 to 4 denier per filament. Changes in conditions other than the temperature, e.g. spinning speed, acetyl value of the triacetate, etc., may alter the exact point of optimum proportions of methylene chloride, but in general the optimum proportions of methylene chloride for any given spinning conditions will be found within about 5% on either side of the straight line described above. Thus, in general, the optimum proportions will be found within the range defined by the equation C=75%T:5,

where C is the concentration of methylene chloride in percent and T is th temperature in degrees centigrade.

The above proportions are on an anhydrous basis. It has been found that the addition of minor amounts of Water does not interfere with the obtaining of optimum properties, though the addition of water above certain levels does affect spinning stability. For example, in one series of tests at 25 C., using a mixture of equal proportions of methylene chloride and methanol, and spinning a 3 denier filament, the addition to the spin bath of 1% and 2 /2 based on the weight of the other components of the spin bath, had little effect on the yarn properties; when the proportion of water was increased to 4% the spinning stability at higher spinning speeds was impaired, but spinning proceeded satisfactorily at lower spinning speeds, i.e. 50 meters per minute.

As stated, the filaments being extruded are stretched in the spin bath. This is done by taking up these filaments at a higher linear speed than the linear speed at which they are extruded. The ratio of these two speeds is known as the draw-down ratio. A suitable range of drawdown ratios is about 15:1 to 35:1, preferably :1 to 5: 1. The actual speed of take up in the process of this invention may be quite high; for example, in excess of 100 meters per minute.

The filaments may b taken up in any desired manner, as by winding them on a driven roll, preferably after they have passed over a driven godet roll outside the spin bath. The spin bath is a good swelling agent for the cellulose triacetate and the filaments leaving the spin bath are swollen with liquid. For best results, at least a portion of this liquid should be removed while the filaments are permitted to undergo some shrinkage in response to the loss of liquid. Such removal of liquid and shrinkage may occur for example during the passage of the filaments from the spin bath to the driven take up roll, at least a portion of the liquid being removed by evaporation during such passage. The removal of the remainder of the liquid may be carried out in any desired manner, as by washing the filaments on the take-up roll, during and after winding, with a non-solvent such as water or isopropanol, followed by drying.

The filaments produced in accordance with this invention are generally of round cross section and are bright in appearance. It will be understood that, if desired, dull filaments may be produced by the incorporation of small amounts of titanium dioxide or other delustering agent into the spinning solution.

In the accompanying drawing,

FIG. 1 is a graph of the results obtained on variation of the proportions in the spin bath in Example II, below; and

FIG. 2 is a photomicrograph of a fiber produced in accordance with the present invention and dried in a manner which did not affect its pebbled surface, the fiber having been shadowed with chromium to show the pebbled surface configuration.

The following examples are given to illustrate this invention further.

Example I A spinning solution containing 24.25% of cellulose triacetate of acetyl value 61.2% and intrinsic viscosity 2.09, dissolved in a solvent mixture of methylene chloride and methanol, the methylene chloridezmethanol ratio being 90.5295, and the viscosity of the solution being 3400 poises (as measured on a Brookfield Synchroelectric Viscometer at 25 C.) is filtered and forced under pressure through a spinning orifice 0.1 mm. in diameter into a spin bath comprising a mixture of methylene chloride and methanol in 48:52 ratio, having a temperature of 26.8 C. The spin bath is circulated slowly in a direction parallel to the movement of the resulting filament. The filament travels through the bath in a generally horizontal direction for 80 cm., then leaves the bath over a rubber guide located at the surface of the bath, then passes through the air above the bath for 32 cm. to a second guide made of Heanium ceramic and then passes through the air for another cm. to a chromium plated guide, from which it travels directly to a driven take up roll, on which it is wound at the rate of meters per minute. The take up roll is mounted so that it lower portion dips into a bath of water which serves to wash the filament on the roll. The resulting substantially solvent-free 3.6 denier filament has a tenacity of 2.0 grams per denier and an elongation of 21.5% at the break. The tension in the running filament, as measured between the Heanium guide and the chromium-plated guide is 318 mg. In this area the running filament is shrinking, despite the tension, due to evaporation of solvent. The draw-down ratio is 5.8:1.

When the above example is repeated, except that the ratio of methylene chloride to methanol in the spin bath is changed to 51:49 the resulting filament has a tenacity of only 1.4 grams per denier and an elongation of 16.5%.

Example II A spinning solution, identical with that of Example I except that the concentration of cellulose triacetate is 21.3% and the viscosity at 25 C. is 2300 poises, is forced under pressure, through a 1 inch diameter spinnerette having 40 orifices each 0.1 mm. in diameter arranged in a single circle of inch radius, into a spin bath composed of a mixture of methylene chloride and methanol at a temperature of 249 C. contained in a tube 3 inches in diameter. The spin bath is passed upward at a slow rate, less than 1 meter per minute, through the tube. The resulting filaments move upward through the spin bath for a distance of 1 meter and are then passed together, as a yarn, through the air for a distance of 3 meters to a take up roll on which the yarn is wound at the rate of 40 meters per minute.

This procedure is repeated, using different proportions of methylene chloride and methanol in the spin bath. The results are shown in the graphs in the drawing. As will be apparent from that drawing, the optimum tenacity and elongation are attained at about the same concentrations of methylene chloride, i.e. 51% and the tenacity and elongation both decrease rapidly as the composition varies from the optimum.

In this example the yarn produced has a denier in the range of 2.5-3 per filament. The draw-down ratio is about 7:1.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patent is:

1. A filamentary material of cellulose triacetate having a tenacity of at least 1.8 grams per denier, an elongation of at least 18% and a pebbled surface.

2. A cellulose triacetate filament exhibiting a tenacity of at least 1.8 grams per denier, an elongation of at least 18%, a pebbled surface, radial uniformity, an overall birefringence above about 0.031 when completely saponified, rubbery properties at 220 C., resistance to creep at 168 C., and substantially no shrinkage on heat treatment.

3. A filamentary material of cellulose triacetate having a tenacity of about 2 grams per denier, an elongation of about 21.5% and a pebbled surface.

4. A filamentary material of cellulose triacetate having a tenacity of about 1.8 to 2 grams per denier and an elongation of about 18% to about 21.5% and a pebbled surface.

5. A filamentary material of cellulose triacetate having a denier below about 4, a tenacity of at least 1.8 grams per denier, an elongation of at least 18% and a pebbled surface.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Dreyfus et a1 May 7, 1935 Dreyfus Jan. 5, 1937 Muller et a1 Jan. 10, 1939 Malm Dec. 3, 1940 Jackson et a1 Apr. 22, 1941 Mehler Jan. 9, 1951 Ladisch Oct. 7, 1952 8 Johnson et a1. Nov. 3, 1953 Ladisc'h Apr. 6, 1954 Tachikawa Jan. 24, 1956 Pedlow Dec. 25, 1956 Wiczer Dec. 2, 1958 Bedell June 9, 1959 FOREIGN PATENTS Great Britain July 25, 1956 

1. A FILAMENTARY MATERIAL OF CELLUULOES TRIACETATE HAVING A TENCITY OF AT LEAST 1.8 GRAMS PER DENIER, AN ELONGATION OF AT LEAST 18% AND A PEBBLE SURFACE. 